Conventionally, a microneedle device has been known as a device for improving transdermal absorption of drugs. A microneedle device includes a microneedle array, and microneedles provided on a base of the microneedle array are intended to pierce the stratum corneum, which is an outermost skin layer, and various sizes and shapes thereof have been proposed. A microneedle device is expected as a non-invasive administration method (for example, see Patent Literature 1).
Further, various methods have also been proposed in regard to a method of applying drugs by use of a microneedle array. Coating the surface of microneedles with drugs, forming a groove or a hollow part in microneedles through which drugs or body components are allowed to penetrate, mixing drugs into microneedles themselves, and the like are known (Patent Literature 2).
Patent Literature 3 states that in a drug transdermal pad base, in a case where fine needles provided on a skin-side surface thereof are made from a biodegradable resin, even if a tip of a fine needle is chipped and remains in skin, the fine needle made from the biodegradable resin is degraded within a living body, thereby causing little adverse effect on the living body, and that as the biodegradable resin, polylactic acid, polyethylene succinate, polybutylene succinate adipate, polybutylene succinate carbonate, polycaprolactone, polyester amide, polyester carbonate, polyvinyl alcohol, polyhydroxy butylate, maltotriose, cellulose, cellulose acetate, collagen, and mixtures thereof are recommended, and polylactic acid or a copolymer of lactic acid and glycolic acid is particularly preferable.
Further, Patent Literature 3 states that in the case of polylactic acid, when its weight average molecular weight is 100,000 to 500,000, an amount thereof deposited to the aforementioned metal thin wire is suitable in view of production, a pulling-out property of the metal thin wire after hardening of the resin is good, and the quality of a finished film (a tubular object) is also excellent. However, Patent Literature 3 does not describe anything about molecular weight and strength.
Patent Literature 4 discloses that in a drug release system which can select and perform any of controlled biphasic release, sustained release, and delayed release, pulverized polylactic acid having a weight average molecular weight of 3000 to 40,000 is used, but it does not describe anything about a microneedle capable of piercing skin at all.